Radiation-curable, acrylated epoxy polymer compositions have been used in various applications in non-particulate states as continuous coatings, films, layers and the like, with subsequent exposure to radiation, as disclosed by the following references.
______________________________________ U.S. Pat. No. Name Date ______________________________________ 4,156,035 Tsao et al. 05-79 4,179,400 Tsao et al. 12-79 4,234,399 McDowell et al. 11-80 4,343,885 Reardon, Jr. 08-82 4,357,219 Sattler 11-82 4,422,914 Tsao et al. 12-83 4,507,383 Tsuruta et al. 03-85 4,937,172 Gervay 06-90 ______________________________________
Tsao et al. U.S. Pat. No. 4,156,035 discloses the use of radiation-curable acrylated epoxy compositions as a continuous layer or coating on various types of substrates with subsequent curing by ultraviolet light. The described compositions are of particular use in curing thick films of acrylated compositions. Gervay U.S. Pat. No. 4,937,172 describes the use of a layered radiation-curable composition with superior adhesion properties for photomasking areas of a substrate. McDowell et al. U.S. Pat. No. 4,234,399 teaches the art of radiation-curable compositions used as continuous film coatings with a desired viscosity. Sattler U.S. Pat. No. 4,357,219 discloses an epoxy coating which is first gelled with ultraviolet light and then cured thermally. It is of particular use in coating wire. Tsuruta et al. U.S. Pat. No. 4,507,383 describes a method of preparing material for a planographic plate which consists of a layer of finely divided solid particles adhering to a substrate. The particulate in this case is typically metallic and is applied in layers to form a rough surface support area for subsequently applied desensitizing agent. The particulate does not become a part of the printed material and is not radiation-cured. Reardon, Jr. U.S. Pat. No. 4,343,885 teaches the use of radiation-curable film epoxies which change color when subjected to radiation and are of particular use as dry photoresist films. Tsao et al. U.S. Pat. No. 4,222,914 describes radiation-curable liquid and solid epoxy compositions. Tsao et al U.S. Pat. No. 4,179,400 discloses a process of using sulfonium salts in radiation-curable epoxy compositions to hasten cudng of the compositions. Formulations of radiation-curable acrylate-modified amineamides are disclosed in the following references.
______________________________________ U.S. Pat. No. Name Date ______________________________________ 4,975,498 Frihart 12-90 4,987,160 Frihart et al. 01-91 5,155,177 Frihart 10-92 5,296,556 Frihart 03-94 ______________________________________
All of these references teach the manufacture of acrylate-modified amineamides for use as a hot melt adhesive. Frihart U.S. Pat. No. 4,975,498 discloses thermally-curable compositions, and Frihart et al. U.S. Pat. No. 4,987,160 teaches actinic radiation-curable compositions for use as hot melt adhesives. Frihart U.S. Pat. No. 5,155,177 and Frihart U.S. Pat. No. 5,296,556 disclose the addition of a reactive diluent to the polyamide, which serves to reduce the viscosity of the polyamide for improved mixing to produce an acrylate-modified polyamide of relatively lower viscosity.
Cationic curing technology involves the photolysis of onium salts and certain other radiation activated compounds. When these materials are irradiated with actinic radiation of the proper wavelength, either Bronstead or Lewis acids are formed. These compounds yield cationic species that cause rapid polymerization of cyloaliphatic epoxides and copolymerization of epoxides and hydroxylic compounds such as glycols, polyols and similar active hydrogen containing compounds, vinyl ethers and other epoxides.
None of the prior art discloses the use of a radiation-curable, solid particulate compositions that can be later cured by exposure to actinic radiation, especially ultraviolet radiation, or radiation generated by a high energy electron beam. The present invention discloses radiation-curable, solid particulate compositions and process for treating the compositions which is of particular use in the art of thermographic printing. Compositions of acrylated polymers, acrylate-modified aminoamides and resins using sulfonium salts are disclosed.
The art of thermography is well known. Following the inking of a substrate, usually a paper sheet, to represent letters, numbers, drawings, and so forth, the inked substrate is covered with a finely ground powder of thermoplastic resin. The resin employed is usually a dimer acid based polyamide polymer that is ground and sifted to a particle size suitable for the size of the print type to be coated. The powder adheres to the wet ink when deposited onto the substrate. Any excess powder can be removed from the substrate. The inked substrate is then heated to a sufficient temperature in order to melt the powder. The particles of the powder flow together to produce the raised print effect. The inked substrate is then cooled whereby the thermoplastic resin reverts back to a solid state and becomes dry.
Thermography is the most flexible and economical way of producing raised print effects. There is no expense for engraved dies as thermography is an allied process to letterpress or offset lithographic printing.
Since the origination of thermography, photocopiers and laser printers have become common equipment for making copies and originals of printed material. Conventional thermoplastic powders used in thermography will melt when processed through high temperature photocopiers and laser printers. The typical melt point of raised print created with conventional thermographic powder is approximately 100 to 130 degrees centigrade. Laser printers and photocopiers operate in a higher temperature range, generally between 200 and 300 degrees centigrade. Consequently, paper that will be processed through this type of high temperature equipment has to be printed without the thermographic effect, or the thermographic raised print effect will be destroyed. The printing industry has expressed the need for the development of heat-resistant raised print to accommodate this high temperature equipment. Such a process is of particular use for the production of letterhead stationary which is used extensively in laser printers and photocopiers.
The present invention discloses radiation-curable, solid particulate compositions and process for treating the compositions so that when they are used as a thermographic powder, the composition will become thermoset and, after being irradiated with actinic radiation, will not remelt again when subjected to the operating temperatures of laser printers and photocopiers.